I'm creating a web app using web.py (although I may later rewrite it for Tornado) which involves a lot of file manipulation. One example, the app will have a git-style 'commit' operation, in which some files are sent to the server and placed in a new folder along with the unchanged files from the last version. This will involve copying the old folder to the new folder, replacing/adding/deleting the files in the commit to the new folder, then deleting all unchanged files in the old folder (as they are now in the new folder).

I've decided on Heroku for the app hosting environment, and I am currently looking at cloud storage options that are built with these kinds of operations in mind. I was thinking of Amazon S3, however I'm not sure if that lets you carry out these kinds of file operations in-place. I was thinking I may have to load these files into the server's RAM and then re-insert them into the bucket, costing me a fortune. I was also thinking of Progstr Filer (http://filer.progstr.com/index.html) but that seems to only integrate with Rails apps.

Can anyone help with this? Basically I want file operations to be as cheap as possible.